1. Field of the Invention
The invention relates to optically transmissive elements and somewhat more particularly to optical ribbon cables or optical flat cables.
2. Prior Art
Electrical flat cables are known and have many advantages in a variety of applications. Typical prior art electrical flat cables or ribbon cables are produced, for example, by lamination, extrusion or calendering techniques or some other similar processes. While such methods are satisfactorily used in instances where such flat cables have metallic conductors therein, they are unsuitable when light conductors, such as optical fibers, are assembled into cables because the prior art production techniques produce mechanical stresses in the light conductors which adversely affect their light transmissive properties; for example, mechanical stresses on a light conductor may cause an increase of the transmission dampening within such a conductor. In addition, such production techniques are relatively rough and provide a relatively high incident of fiber breakage. Further, extruded members usually have orientation stresses, causing undesirable force influences on so-produced optical elements.
Optical cables which are embodied in the manner of electrical ribbon cables are known wherein a plurality of optical fibers are positioned next to one another in a parallel relation and are encased or enveloped between two interlaminated or interfused foils or sheets. The foils function as carriers for the optical fibers and can be further processed so as to form a cable in the form of an electrical ribbon cable. For example, such encased optical fibers can be positioned onto a cable core in an axially parallel relation, in a spiral relation, formed into a tube and placed onto a cable core or formed into a strand and positioned as a strand element in a body. Further details of this type of optical cable structure can be obtained from German Offenlegungsschrifts Nos. 2,314,313 or 2,424,041 or from U.S. Pat. No. 3,883,218.